The present invention relates to a tapered roller bearing used in a driving unit of a rolling mill or a railway vehicle. Particularly, the present invention relates to an improvement in prevention of seizure between a large rib surface and roller large-diameter-side end surfaces of a tapered roller bearing used as a thrust bearing of a rolling mill operating at a high rotating velocity, a pinion of a driving unit of a railway vehicle, or the like.
Conventionally, tapered roller bearings have been used for thrust bearings of rolling mills, driving unit pinion bearings of railway vehicles, and so on.
FIG. 4 and FIG. 5 are conceptual diagrams showing a contact state between a large rib surface 2a of an inner ring 2 and a large-diameter-side end surface 3a of a roller 3 in a tapered roller bearing. When an axial load acts on the tapered roller bearing (see the arrows Fa in FIG. 1), the load is partially given to the large-diameter-side end surface 3a of the roller 3 and the large rib surface 2a of the inner ring. As a result, pressure distribution as shown in FIG. 6 is produced in a contact ellipse 32 in a contact position (e.sub.0) where the large rib surface 2a of the inner ring contacts with the large-diameter-side end surface of the roller 3 as shown in FIG. 5.
Note that in FIG. 6, a designates a long diameter of a contact ellipse between the inner ring large rib surface and the roller large-diameter-side end surface, and also b denotes a short diameter of the contact ellipse between the inner ring large rib surface and the roller large-diameter-side end surface.
In addition, there is a difference in velocity between the inner ring 2 and the roller 3 at the contact position (e.sub.0) where the large rib surface 2a of the inner ring 2 contacts with the large-diameter-side end surface of the roller 3.
On the assumption that there is no slip in a plane where a race surface (so called as a race track) of the inner ring contacts with a rolling surface of the roller, the relative velocity (V.sub.i) between the circumferential velocity (X) of the race surface of the inner ring and the revolution velocity (Y) of the roller on the race surface of the inner ring is equal to the circumferential rotation velocity (V.sub.R) of the rolling surface of the roller. However, the contact position circumferential velocity (V.sub.i ') of the inner ring large rib surface is larger than the contact position circumferential velocity (V.sub.R ') of the roller large-diameter-side end surface, so that such a slip as represented by (Vs) in FIG. 7 is generated.
Note that the above-mentioned the circumferential velocity (X) of the race surface of the inner ring, the revolution velocity (Y) of the roller on the race surface of the inner ring, the relative velocity (V.sub.i) between the circumferential velocity (X) and the revolution velocity (Y), the circumferential rotation velocity (V.sub.R) of the rolling surface of the roller, the contact position circumferential velocity (V.sub.i ') of the inner ring large rib surface, the contact position circumferential velocity (V.sub.R ') of the roller large-diameter-side end surface, and the slip velocity (Vs) of the slippage respectively satisfy following equations(1)-(8): EQU X=r.sub.i .multidot..omega..sub.i (1) EQU Y=r.sub.i .multidot..omega..sub.c (2) EQU Vi=r.sub.i (.omega..sub.i -.omega..sub.c) (3) EQU V.sub.R =r.sub.R .multidot..omega..sub.R (4) EQU Vi=V.sub.R (5) EQU Vi'=(r.sub.i +e).multidot.(.omega..sub.i -.omega..sub.c) (6) EQU V.sub.R '=(r.sub.R +e).multidot..omega..sub.R (7) EQU Vs=Vi'-V.sub.R (8)
where e.sub.0 expresses a contact point between the inner ring large rib surface and a roller large-diameter-side end surface; e defines a contact position height; r.sub.i denotes a radius of an race surface of a large diameter portion of the inner ring; r.sub.R defines a radius on the large diameter side of the roller; 107 .sub.i expresses an angular velocity of the inner ring; .omega..sub.c defines revolution angular velocity of the roller; and .omega..sub.R denotes rotation angular velocity of the roller.
When the bearing pressure or the slip velocity increased in this contact position (e.sub.0), there was a case where seizure was caused in the position in accordance with state of lubrication. When this position was seized, a smooth rotating function of the bearing was spoiled, it might occasionally cause a trouble on the whole of a mechanical equipment. Therefore, in order to cope with this problem, there have been taken such measures that the state of lubrication is improved, the pressure in the contact plane is reduced, or the slip velocity at the contact position is reduced.
However, in the conventional tapered roller bearing, a large space was required by a groove-like recess 21 in the inner ring large rib as shown in FIG. 8 or a large-diameter-side end surface chamfer C1 of the roller 3 as shown in FIG. 9. Accordingly, if the area of the contact ellipse was increased to reduce the bearing pressure to a small value, a lower (inner ring orbit side) contact ellipse 32 at the contact position (e.sub.0) expanded to the groove-like recess 21 of the inner ring large rib, thereby causing a problem that a peak of the bearing pressure was generated at the circumferential edge of the groove-like recess, or, if the contact position (e.sub.0) is shifted to a higher place in order to prevent the peak generation, the slip velocity Vs increases.
In addition, the groove-like recess 21 in the inner ring large rib surface 2a has a connection with the strength of the large rib surface 2a. If the recess 21 is made extremely small, stress concentration is caused. It is therefore necessary to make the recess 21 have an enough size not to reduce the strength of the large rib surface 2a. Even if the recess 21 of the inner ring large rib is made as small as possible, if the chamfer (C1) of the large-diameter-side end surface of the roller is left large as it is, the contact ellipse 32 projects from the chamfer (C1) of the large-diameter-side end surface of the roller in the same manner as described above, so that a peak of the bearing pressure is generated at the circumferential edge of the chamfer of the roller.